CAN A PATCHY POPULATION STRUCTURE AFFECT THE EVOLUTION OF COMPETITION STRATEGIES?

Simulation models are described that examine the effect of a patchy population structure on the evolution of competition strategies. The results of the models suggest that a patchy population structure will make the evolution of scramble competition strategies more likely than in a single undivided population. The outcome of the models depends on the details of the population structure, in particular the number of individuals that found patches, the number of generations of competition within a patch, and the point at which founding females mate can all affect the evolutionary outcome. The results of the models are compared to those of previous models examining the effects of a structured population on the evolution of female-biased sex ratios, and altruistic behavior. The results of the model may help to explain the patterns of larval competition strategies observed in bruchid beetles.     

SOCIAL SELECTION AND THE EVOLUTION OF ANIMAL SIGNALS

Social selection is presented here as a parallel theory to sexual selection and is defined as a selective force that occurs when individuals change their own social behaviors, responding to signals sent by conspecifics in a way to influence the other individuals' fitness. I analyze the joint evolution of a social signal and behavioral responsiveness to the signal by a quantitative-genetic model. The equilibria of average phenotypes maintained by a balance of social selection and natural selection and their stability are examined for two alternative assumptions on behavioral responsiveness, neutral and adaptive. When behavioral responsiveness is neutral on fitness, a rapid evolution by runaway selection occurs only with enough genetic covariance between the signal and responsiveness. The condition for rapid evolution also depends on natural selection and the number of interacting individuals. When signals convey some information on signalers (e.g., fighting ability), behavioral responsiveness is adaptive such that a receiver's fitness is also influenced by the signal. Here there is a single point of equilibrium. The equilibrium point and its stability do not depend on the genetic correlation. The condition needed for evolution is that the signal is beneficial for receivers, which results from reliability of the signal. Frequency-dependent selection on responsiveness has almost no influence on the equilibrium and the rate of evolution.     

ON OPTIMAL LEARNING SCHEDULES AND THE MARGINAL VALUE OF CUMULATIVE CULTURAL EVOLUTION

The age‐dependent choice between expressing individual learning (IL) or social learning (SL) affects cumulative cultural evolution. A learning schedule in which SL precedes IL is supportive of cumulative culture because the amount of nongenetically encoded adaptive information acquired by previous generations can be absorbed by an individual and augmented. Devoting time and energy to learning, however, reduces the resources available for other life‐history components. Learning schedules and life history thus coevolve. Here, we analyze a model where individuals may have up to three distinct life stages: “infants” using IL or oblique SL, “juveniles” implementing IL or horizontal SL, and adults obtaining material resources with learned information. We study the dynamic allocation of IL and SL within life stages and how this coevolves with the length of the learning stages. Although no learning may be evolutionary stable, we find conditions where cumulative cultural evolution can be selected for. In that case, the evolutionary stable learning schedule causes individuals to use oblique SL during infancy and a mixture between IL and horizontal SL when juvenile. We also find that the selected pattern of oblique SL increases the amount of information in the population, but horizontal SL does not do so.     

人口与社会-经济-自然复合生态系统的持续发展——伊春市人口的系统分析与调控对策

本文讨论了人口与社会-经济-自然复合生态系统持续发展的关系,指出了人口问题是决定复合生态系统持续发展的关键因素。只有人口与复合生态系统的各个方面相互适应,复合生态系统持续发展的目标才能得以实现。本文以伊春市为实例,系统地分析了伊春人口的发展过程,采用系统动力学的方法,建立了伊春人口的系统动力学模型,并以此模型对伊春人口进行了系统仿真和预测,同时提出了解决伊春人口问题的调控对策。     

HOST POPULATION STRUCTURE AND THE EVOLUTION OF VIRULENCE: A “LAW OF DIMINISHING RETURNS”

Structure in a population of host individuals, whether spatial or temporal, can have important effects on the transmission and evolutionary dynamics of its pathogens. One of these is to limit dispersal of pathogens and thus increase the amount of contact between a given pair or within a small group of host individuals. We introduce a “law of diminishing returns” that predicts an evolutionary decline of pathogen virulence whenever there are on average more possibilities of pathogen transmission between the same pair of hosts. Thus, the effect of repeated contact between hosts will be to shift the balance of any trade-off between virulence and transmissibility toward lower virulence.     

THE POPULATION GENETICS OF ADAPTATION: THE DISTRIBUTION OF FACTORS FIXED DURING ADAPTIVE EVOLUTION

We know very little about the genetic basis of adaptation. Indeed, we can make no theoretical predictions, however heuristic, about the distribution of phenotypic effects among factors fixed during adaptation nor about the expected “size” of the largest factor fixed. Study of this problem requires taking into account that populations gradually approach a phenotypic optimum during adaptation via the stepwise substitution of favorable mutations. Using Fisher's geometric model of adaptation, I analyze this approach to the optimum, and derive an approximate solution to the size distribution of factors fixed during adaptation. I further generalize these results to allow the input of any distribution of mutational effects. The distribution of factors fixed during adaptation assumes a pleasingly simple, exponential form. This result is remarkably insensitive to changes in the fitness function and in the distribution of mutational effects. An exponential trend among factors fixed appears to be a general property of adaptation toward a fixed optimum.     

EVOLUTION AND POPULATION STRUCTURE OF AFRICANIZED HONEY BEES IN BRAZIL: EVIDENCE FROM SPATIAL ANALYSIS OF MORPHOMETRIC DATA

In recent years, studies based on isoenzymatic patterns of geographic variation have revealed that what is usually called the Africanized honey bee does not constitute a single population. Instead, several local populations exist with various degrees of admixture with European honey bees. In this paper, we evaluated new data on morphometric patterns of Africanized honey bees collected at 42 localities in Brazil, using univariate and multivariate (canonical) trend surface and spatial autocorrelation analyses. The clinal patterns of variation found for genetically independent characters (wing size characters and some wing venation angles) are concordant with previous studies of malate dehydrogenase (MDH) allelic frequencies and support the hypothesis that larger honey bees in southern and southeastern Brazil originated by racial admixture in the initial phases of African honey bee colonization. Geographic variation patterns of Africanized honey bee populations reflect a demic diffusion process in which European genes were gradually lost because of the higher fitness of the African gene pool in Neotropical environmental conditions.     

GROUP FORMATION AND THE EVOLUTION OF SOCIALITY

In spite of its intrinsic evolutionary instability, altruistic behavior in social groups is widespread in nature, spanning from organisms endowed with complex cognitive abilities to microbial populations. In this study, we show that if social individuals have an enhanced tendency to form groups and fitness increases with group cohesion, sociality can evolve and be maintained in the absence of actively assortative mechanisms such as kin recognition or nepotism toward other carriers of the social gene. When explicitly taken into account in a game‐theoretical framework, the process of group formation qualitatively changes the evolutionary dynamics with respect to games played in groups of constant size and equal grouping tendencies. The evolutionary consequences of the rules underpinning the group size distribution are discussed for a simple model of microbial aggregation by differential attachment, indicating a way to the evolution of sociality bereft of peer recognition.     

FEMALE-BIASED SEX RATIOS IN A FACULTATIVELY SOCIAL BEE AND THEIR IMPLICATIONS FOR SOCIAL EVOLUTION

Montane populations of the Australian allodapine bee, Exoneura bicolor, are characterized by high levels of cooperative nesting and strongly female-biased sex ratios. A conspecific population from heathland shows much lower levels of cooperative nesting and lower levels of female bias. In both habitats, sex-ratio bias is greatest in the smallest brood sizes and becomes successively less biased in larger broods. Parity is approached in the largest heathland colonies, but not for any brood-size category in montane areas. Adult intracolony relatedness is moderately high for colonies in both reused and newly founded nests in the montane habitat, but probably low or zero for newly founded nests in heathland. Colony efficiency, measured as the number of brood per adult, increases with colony size in both habitats, suggesting that cooperation between females increases mean female fitness. It is argued that patterns of sex allocation are consistent with nonlinear fitness-return models, in which the mean reproductive value of daughters increases with the number of daughters produced in a brood. Such increases probably arise from a number of social interactions, including cooperative brood defense, increased task efficiency, and lower per capita costs in nest construction. The term “local fitness enhancement” is introduced here to describe these effects collectively. The female-biased ratios should lower selective thresholds for sib-directed altruism, at least in the earlier stages of colony development. It is argued that local fitness enhancement facilitates eusociality in allodapine bees and could also play a role in other haplodiploid taxa, provided cooperative nesting largely involves sisters, colony efficiency increases with colony size, and optimal colony sizes are only achieved after two or more generations after founding.     

SIZE VARIATION,GROWTH STRATEGIES,AND THE EVOLUTION OF MODULARITY IN THE MAMMALIAN SKULL

Allometry is a major determinant of within‐population patterns of association among traits and, therefore, a major component of morphological integration studies. Even so, the influence of size variation over evolutionary change has been largely unappreciated. Here, we explore the interplay between allometric size variation, modularity, and life‐history strategies in the skull from representatives of 35 mammalian families. We start by removing size variation from within‐species data and analyzing its influence on integration magnitudes, modularity patterns, and responses to selection. We also carry out a simulation in which we artificially alter the influence of size variation in within‐taxa matrices. Finally, we explore the relationship between size variation and different growth strategies. We demonstrate that a large portion of the evolution of modularity in the mammalian skull is associated to the evolution of growth strategies. Lineages with highly altricial neonates have adult variation patterns dominated by size variation, leading to high correlations among traits regardless of any underlying modular process and impacting directly their potential to respond to selection. Greater influence of size variation is associated to larger intermodule correlations, less individualized modules, and less flexible responses to natural selection.     

SELFISH LARVAE: DEVELOPMENT AND THE EVOLUTION OF PARASITIC BEHAVIOR IN THE HYMENOPTERA

Queens of hymenopteran social parasites manipulate the workers of other social species into raising their offspring. However, nonconspecific brood care may also allow the parasite larvae to control their own development to a greater extent than possible in nonparasitic species. An evolutionary consequence of this may be the loss of the parasite's worker caste if the larvae can increase their fitness by developing into sexuals rather than workers. We argue that this loss is particularly likely in species in which there is little inclusive fitness benefit in working. Retention of a worker caste correlates with characteristics that increase the fitness of working relative to becoming a sexual, such as worker-production of males, high intracolony relatedness, and seasonal environments where the hosts of potential parasite queens are not always available. Further evidence strongly suggests that when the worker caste is evolutionarily lost in perennial species like ants, it disappears rapidly and through a reduction in caste threshold and queen size, so that parasite larvae become queens with less food than required to produce host workers. This evolutionary process, however, appears to lower overall population fitness, resulting in workerless parasite species having small populations and being geographically restricted. Conversely, in annual species like bees and wasps, workerless social parasitism evolves with no size reduction in queens, which is consistent with an expected lower level of queen/offspring conflict.     

THE EVOLUTION OF SOCIAL SIGNALS: MORPHOLOGICAL,FUNCTIONAL, AND GENETIC INTEGRATION OF THE SEX PHEROMONE IN NAUPHOETA CINEREA

Social signals that mediate intraspecific interactions can be complex, conveying considerable information concerning the probable behavior of individuals and minimizing overt aggression and wasted energy. In the cockroach Nauphoeta cinerea, male-male competition and female mate choice are mediated by a multicomponent male-produced sex pheromone. In this study, I examine variation in this pheromone. First I measure differences among males in both individual pheromone compounds and the overall composition of the pheromone. Principal component analysis is used to quantify and describe pheromone composition. Next, I explore some of the causes and consequences of this variation by examining the pheromone of males with different social experiences. Compared to subordinate males, dominant males have significantly less variable quantities of the individual pheromone compounds and are significantly less variable in the composition of their pheromone. Because of an association between status and mating success, male-male competition can result in stabilizing sexual selection on the sex pheromone. Finally, I test the hypothesis that the pheromone compounds evolve in a manner consistent with their function. As predicted for morphologically integrated characters, the patterns of phenotypic, genetic, and environmental correlations among my measures of pheromone compounds and composition match functional patterns suggested by this study and the developmental patterns demonstrated in my previous studies. Based on these studies of the N. cinerea sex pheromone, I argue that stabilizing sexual selection shapes the evolution of pheromonal communication involved in social interactions among male N. cinerea. Further, I argue that coordinated evolution of social signals may be possible due to the morphological integration of their multiple compounds.     

灵芝对小鼠空间分辨学习与记忆的影响

本文用Y-型迷宫法测试小鼠空间分辨行为。实验结果表明,每日ig灵芝2.58/kg共7d,有明显促进学习的作用。每日ig灵芝2.5g/kg共7d或ig灵芝5g/kg共7d都能显著地拮坑东莨菪碱所致学习障碍的作用。此外,学习训练后立即ig灵芝2.5g/kg或ig灵芝5g/kg也有明显地改善东莨菪碱损害记忆巩固的作用。     

THE EVOLUTION OF SPITE: POPULATION STRUCTURE AND BACTERIOCIN‐MEDIATED ANTAGONISM IN TWO NATURAL POPULATIONS OF XENORHABDUS BACTERIA

Spite occurs when an individual harms itself in the act of harming other individuals. Such behaviors were once assumed to be of limited evolutionary importance, as the conditions for the evolution of spite were thought to be too restrictive. Recent theoretical work, however, suggests that spatial population structure, which allows local competition among genotypes, could favor the evolution of spite. One of the clearest examples of spite is the costly production and release by bacteria of toxins (called bacteriocins) that can kill unrelated strains of the same species. Here, we establish the existence of spatial structure in two natural populations of bacteriocin‐producing bacteria. Specifically, relatedness decreased with increasing spatial distance between the field isolates. In addition, toxin‐mediated inhibitions were found only between isolates that were collected more than 1 m apart and that were generally less than 80% similar in their genomic fingerprints. Taken together, the results suggest that the bacteria are spatially structured, with mixing of genotypes and spiteful interactions at the boundaries between demes.     

INTERACTING PHENOTYPES AND THE EVOLUTIONARY PROCESS: I. DIRECT AND INDIRECT GENETIC EFFECTS OF SOCIAL INTERACTIONS

Interacting phenotypes are traits whose expression is affected by interactions with conspecifics. Commonly-studied interacting phenotypes include aggression, courtship, and communication. More extreme examples of interacting phenotypes—traits that exist exclusively as a product of interactions—include social dominance, intraspecific competitive ability, and mating systems. We adopt a quantitative genetic approach to assess genetic influences on interacting phenotypes. We partition genetic and environmental effects so that traits in conspecifics that influence the expression of interacting phenotypes are a component of the environment. When the trait having the effect is heritable, the environmental influence arising from the interaction has a genetic basis and can be incorporated as an indirect genetic effect. However, because it has a genetic basis, this environmental component can evolve. Therefore, to consider the evolution of interacting phenotypes we simultaneously consider changes in the direct genetic contributions to a trait (as a standard quantitative genetic approach would evaluate) as well as changes in the environmental (indirect genetic) contribution to the phenotype. We then explore the ramifications of this model of inheritance on the evolution of interacting phenotypes. The relative rate of evolution in interacting phenotypes can be quite different from that predicted by a standard quantitative genetic analysis. Phenotypic evolution is greatly enhanced or inhibited depending on the nature of the direct and indirect genetic effects. Further, unlike most models of phenotypic evolution, a lack of variation in direct genetic effects does not preclude evolution if there is genetic variance in the indirect genetic contributions. The available empirical evidence regarding the evolution of behavior expressed in interactions, although limited, supports the predictions of our model.     

小麦的分类、起源与进化

小麦是世界历史上最古老的作物之一,约在一万年以前,在西南亚,人类首先成功地将小麦进行栽培生产粮食,因此小麦栽培历史和人类开化有着密切的相互关系。在现代世界农业中,小麦也是最重要的作物之一。它分布面积很广,从北纬67°的挪威、芬兰和苏联到南纬45°的阿根庭都有栽培。世界生产小麦的地区有苏联南部、美国中部平     

INTERACTING PHENOTYPES AND THE EVOLUTIONARY PROCESS. III. SOCIAL EVOLUTION

Interactions among conspecifics influence social evolution through two distinct but intimately related paths. First, they provide the opportunity for indirect genetic effects (IGEs), where genes expressed in one individual influence the expression of traits in others. Second, interactions can generate social selection when traits expressed in one individual influence the fitness of others. Here, we present a quantitative genetic model of multivariate trait evolution that integrates the effects of both IGEs and social selection, which have previously been modeled independently. We show that social selection affects evolutionary change whenever the breeding value of one individual covaries with the phenotype of its social partners. This covariance can be created by both relatedness and IGEs, which are shown to have parallel roles in determining evolutionary response. We show that social selection is central to the estimation of inclusive fitness and derive a version of Hamilton's rule showing the symmetrical effects of relatedness and IGEs on the evolution of altruism. We illustrate the utility of our approach using altruism, greenbeards, aggression, and weapons as examples. Our model provides a general predictive equation for the evolution of social phenotypes that encompasses specific cases such as kin selection and reciprocity. The parameters can be measured empirically, and we emphasize the importance of considering both IGEs and social selection, in addition to relatedness, when testing hypotheses about social evolution.     

小麦的分类、起源与进化

小麦是世界历史上最古老的作物之一,约在一万年以前,在西南亚,人类首先成功地将小麦进行栽培生产粮食,因此小麦栽培历史和人类开化有着密切的相互关系。在现代世界农业中,小麦也是最重要的作物之一。它分布面积很广,从北纬67°的挪威、芬兰和苏联到南纬45°的阿根庭都有栽培。世界生产小麦的地区有苏联南部、美国中部平原和加拿大相邻地区、地中海地区、中国、印度、阿根廷北部和澳大利亚的西南部。这类作物在比较宽的环境 范围内都能获得高产。据统计,全世界有1/3的人口以小麦为主要粮食.消费的小麦食物卡值占全世界的20%以上。     

THE EVOLUTION OF CANALIZATION AND THE BREAKING OF VON BAER'S LAWS: MODELING THE EVOLUTION OF DEVELOPMENT WITH EPISTASIS

Evolution can change the developmental processes underlying a character without changing the average expression of the character itself. This sort of change must occur in both the evolution of canalization, in which a character becomes increasingly buffered against genetic or developmental variation, and in the phenomenon of closely related species that show similar adult phenotypes but different underlying developmental patterns. To study such phenomena, I develop a model that follows evolution on a surface representing adult phenotype as a function of underlying developmental characters. A contour on such a “phenotype landscape” is a set of states of developmental characters that produce the same adult phenotype. Epistasis induces curvature of this surface, and degree of canalization is represented by the slope along a contour. I first discuss the geometric properties of phenotype landscapes, relating epistasis to canalization. I then impose a fitness function on the phenotype and model evolution of developmental characters as a function of the fitness function and the local geometry of the surface. This model shows how canalization evolves as a population approaches an optimum phenotype. It further shows that under some circumstances, “decanalization” can occur, in which the expression of adult phenotype becomes increasingly sensitive to developmental variation. This process can cause very similar populations to diverge from one another developmentally even when their adult phenotypes experience identical selection regimes.